I have a 1999 Blazer and here is how it started. The ABS would engage when stopping sometimes and you would have to let off the brakes and apply them again to stop. The ABS light would come on and then go off. This would happen about 2 to 3 times a month. Now the ABS light is off but the brake pedal goes to the floor but it will stop you. I tried to bleed the back brakes and I get no air or fluid to the backs. I stopped there and wanted to ask for advice before I did anything else. Why am I not getting anything to the rear brakes.

 

I'm not an expert as I have just learned the brakes portion in my automotive class but I'm guessing it is probably your proportioning valve.

 

Exactly-But a total system flush&bleed will be advisable as well!